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textbook:nrctextbook:chapter16 [2025-05-05 11:15]
Merja Herzig 		textbook:nrctextbook:chapter16 [2025-05-07 14:06] (current)
Merja Herzig
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 {{anchor:radiochemical_purity}} {{anchor:radiochemical_purity}}
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 ===== 16.3. Radiochemical and radionuclidic purity ===== ===== 16.3. Radiochemical and radionuclidic purity =====
  
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-When a tracer experiment with a certain radionuclide is done it is most often desirable that there are not any other radionuclides present since measurement of single radionuclide is easier as no radiochemical separations nor spectrometric analysis are needed. When a tracer product contains only one specific radionuclide, it is called radionuclidic pure. Radionuclide purity as a measure means the activity fraction of a specific radionuclide of the total activity. To produce radionuclidic  +When a tracer experiment with a certain [[textbook:nrctextbook:chapter4|radionuclide]] is done it is most often desirable that there are not any other radionuclides present since measurement of single radionuclide is easier as no radiochemical separations nor spectrometric analysis are needed. When a tracer product contains only one specific radionuclide, it is called radionuclidic pure. Radionuclide purity as a measure means the activity fraction of a specific radionuclide of the total activity. To produce radionuclidic pure tracers by [[textbook:nrctextbook:chapter15|nuclear reactions]] is not an easy task. The conditions in production reactions, particularly [[textbook:nrctextbook:chapter15#projectile_particle|projectile]] energy and bombardment time, should be kept so that only one product nuclide is observed. This is, however, not typically possible since the [[textbook:nrctextbook:chapter15#cross_section|cross sections]] of various reactions overlap in [[textbook:nrctextbook:chapter15#excitation_function|excitation function]]. For example, if <sup>209</sup>Po tracer is produced in [[textbook:nrctextbook:chapter16#cyclotrons|cyclotron]] by bombarding <sup>209</sup>Bi with [[textbook:nrctextbook:chapter2#deuterium|deuterons]] by the reaction ${}^{209}\mathrm{Bi}(d, 2n){}^{209}\mathrm{Po}$ the optimum deuteron energy of about 15 MeV, resulting in the highest yield, may not be used due to coproduction of <sup>208</sup>Po. Instead, somewhat lower deuteron energies should be applied to minimize the fraction of <sup>208</sup>Po (Fig. XVII.1).
-pure tracers by nuclear reactions is not an easy task. The conditions in production reactions, particularly projectile energy and bombardment time, should be kept so that only one product nuclide is observed. This is, however, not typically possible since the cross sections of various reactions overlap in excitation function. For example, if <sup>209</sup>Po tracer is produced in cyclotron by bombarding <sup>209</sup>Bi with deuterons by the reaction ${}^{209}\mathrm{Bi}(d, 2n){}^{209}\mathrm{Po}$ the optimum deuteron energy of about 15 MeV, resulting in the highest yield, may not be used due to coproduction of <sup>208</sup>Po. Instead somewhat lower deuteron energies should be applied to minimize the fraction of <sup>208</sup>Po (Fig. XVII.1).+
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-Another critical factor in producing radionuclidic pure tracers is the purity of the target material. Even very low amounts of impurities may result in considerable amounts of undesired radionuclides in the product, especially in case where the impurity atoms have higher cross sections for the used projectiles than the actual target atoms. To avoid formation of undesired radionuclides elementally very pure targets are typically needed. In some cases elementally pure targets are not enough to  +Another critical factor in producing //radionuclidic pure// tracers is the purity of the [[textbook:nrctextbook:chapter15#target_nucleus|target material]]. Even very low amounts of impurities may result in considerable amounts of undesired [[textbook:nrctextbook:chapter4|radionuclides]] in the product, especially in case where the impurity atoms have higher [[textbook:nrctextbook:chapter15#cross_section|cross sections]] for the used [[textbook:nrctextbook:chapter15#projectile_particle|projectiles]] than the actual target atoms. To avoid formation of undesired radionuclides elementally very pure targets are typically needed. In some cases, elementally pure targets are not enough to prevent formation of undesired radionuclides, but even isotopically pure targets are needed. For example, in the production of <sup>18</sup>F by the reaction ${}^{18}\mathrm{O}(p,n){}^{18}\mathrm{F}$ water enriched with respect to <sup>18</sup>O is used as the target. The enrichment of <sup>18</sup>O in the target water is about 97% while in the natural water it is only 0.2%. Isotopically pure target materials may be very expensive.
-prevent formation of undesired radionuclides but even isotopically pure targets are needed. For example, in the production of 18F by the reaction ${}^{18}\mathrm{O}(p,n){}^{18}\mathrm{F}$ water enriched with respect to <sup>18</sup>O is used as the target. The enrichment of 18O in the target water is about 97% while in the natural water it is only 0.2%. Isotopically pure target materials may be very expensive.+
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-In addition to radionuclidic purity another term, radiochemical purity is important, particularly in labelling of organic molecules, for radiopharmaceutical purpose for example. Radiochemically pure compounds are the desired compounds containing the radionuclide or the compounds containing the radionuclide in a desired position. In, for example, <sup>18</sup>F-labelled radiopharmaceutical 2-FDG (2-deoxy-2-[<sup>18</sup>F]fluoro-D-g1ucose) product the radiochemically impure compounds are those where the <sup>18</sup>F-label is somewhere else than in 2-deoxy position or other 18F-labelled compounds, such as tetra-acetyl-2-[<sup>18</sup>F]FDG.+In addition to radionuclidic purity another term, //radiochemical purity// is important, particularly in labelling of organic molecules, for radiopharmaceutical purpose for example. Radiochemically pure compounds are the desired compounds containing the radionuclide or the compounds containing the radionuclide in a desired position. In, for example, <sup>18</sup>F-labelled radiopharmaceutical 2-FDG (2-deoxy-2-[<sup>18</sup>F]fluoro-D-glucose) product the radiochemically impure compounds are those where the <sup>18</sup>F-label is somewhere else than in 2-deoxy position or other <sup>18</sup>F-labelled compounds, such as tetra-acetyl-2-[<sup>18</sup>F]FDG.
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 {{anchor:radionuclide_generators}} {{anchor:radionuclide_generators}}
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 Radionuclide tracers are commercially typically available as liquids containing radionuclides as ions, for example <sup>137</sup>CsCl and NH<sub>4</sub>H<sup>32</sup>PO<sub>4</sub> or as labelled compounds, such as [methyl- Radionuclide tracers are commercially typically available as liquids containing radionuclides as ions, for example <sup>137</sup>CsCl and NH<sub>4</sub>H<sup>32</sup>PO<sub>4</sub> or as labelled compounds, such as [methyl-
-<sup>14</sup>C]methionine and [<sup>35</sup>S]methionine. A number of radionuclide tracers are available in a mode of generator. In these a radionuclide, produced either in a reactor or a cyclotron, is trapped in column containing a sorbent, such as alumina, capable of sorbing this radionuclide. In the column the sorbed radionuclide decays to its daughter nuclide which is the desired tracer nuclide. The sorbent  +<sup>14</sup>C]methionine and [<sup>35</sup>S]methionine. A number of radionuclide tracers are available in a mode of generator. In these a radionuclide, produced either in a [[textbook:nrctextbook:chapter16#radionuclide_production_reactors|reactor]] or a [[textbook:nrctextbook:chapter16#cyclotrons|cyclotron]], is trapped in column containing a sorbent, such as alumina, capable of sorbing this radionuclide. In the column the sorbed radionuclide decays to its daughter nuclide which is the desired tracer nuclide. The sorbent needs to efficiently trap the parent nuclide but not the daughter which should be eluteable out from the column while the parent nuclide remains. Another requirement is that the [[textbook:nrctextbook:chapter6#half_life|half-life]] of the daughter is shorter than that of the parent; otherwise no radiochemical [[textbook:nrctextbook:chapter6#activity_equilibrium|equilibrium]] would be attained in the column.
-needs to efficiently trap the parent nuclide but not the daughter which should be eluteable out from the column while the parent nuclide remains. Another requirement is that the half-life of the daughter is shorter than that of the parent; otherwise no radiochemical equilibrium would be attained in the column.+
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-As examples of radionuclide generators the 99mTc and 137mBa generators are described. In a Tc generator the parent <sup>99</sup>Mo (t½ = 66 h), produced in a reactor by neutron activation of stable <sup>98</sup>Mo, is trapped in an aluminum oxide column where it decays to a short-lived <sup>99m</sup>Tc (t½ = 6.0 h). Tc forms an anionic TcO<sub>4</sub><sup>-</sup> ion that can be eluted from the column with NaCl solution while <sup>99</sup>Mo remains in the column as MoO<sub>4</sub><sup>2-</sup>. <sup>99m</sup>Tc is widely used as a radiopharmaceutical in hospitals in single photon  +As examples of radionuclide generators, the <sup>99m</sup>Tc and <sup>137m</sup>Ba generators are described. In a Tc generator the parent <sup>99</sup>Mo (t½ = 66 h), produced in a [[textbook:nrctextbook:chapter16#radionuclide_production_reactors|reactor]] by [[textbook:nrctextbook:chapter15#neutron_capture|neutron activation]] of stable <sup>98</sup>Mo, is trapped in an aluminum oxide column where it [[textbook:nrctextbook:chapter5|decays]] to a short-lived <sup>99m</sup>Tc (t½ = 6.0 h). Tc forms an anionic TcO<sub>4</sub><sup>-</sup> ion that can be eluted from the column with NaCl solution while <sup>99</sup>Mo remains in the column as MoO<sub>4</sub><sup>2-</sup>. <sup>99m</sup>Tc is widely used as a radiopharmaceutical in hospitals in single photon tomography imaging of humans. <sup>99m</sup>Tc emits fairly energetic [[textbook:nrctextbook:chapter5#gamma|gamma rays]] (143 keV) which can be readily detected with [[textbook:nrctextbook:chapter9|gamma detectors]].
-tomography imaging of humans. <sup>99m</sup>Tc emits fairly energetic gamma rays (143 keV) which can be readily detected with gamma detectors.+
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textbook/nrctextbook/chapter16.1746436543.txt.gz · Last modified: 2025-05-05 11:15 by Merja Herzig

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